Evaluation of Nitrogen Removal Capacity in a Pilot-scale Two-stage Partial Nitritation-ANAMMOX Process Seeded with Activated Sludge

Digester supernatant containing high nitrogen concentrations often destabilizes conventional nitrification- denitrification processes, creating the need for energy-efficient biological nitrogen removal technologies such as partial nitritation (PN)/anaerobic ammonium oxidation (Anammox) process (PN/A). This study established a pilot-scale PN/A system composed of a 10m3 partial nitritation reactor and a 10m3 Anammox reactor using real digester supernatant. The partial nitritation reactor achieved a NAR of 1.0 within 10 days and maintained stable nitrite accumulation during continuous operation, with an average NAR of 0.9±0.1. Specific NOB (Nitrite-oxidizing bacteria) activity decreased from 4.288 to 0.971mgN/g VSS/d during start-up, confirming effective NOB suppression. In the Anammox reactor, simultaneous NH4+-N and NO2--N consumption appeared after the fed-batch phase, and the specific Anammox activity increased from 0.13 to 0.64gN/g VSS/d, indicating successful enrichment of Anammox. The maximum nitrogen removal rate reached 0.62kgN/m3/d. Although partial nitritation performance was temporarily inhibited by elevated influent heavy metals, complete recovery occurred within one week after influent replacement. These results demonstrate that a two-stage PN/A configuration provides high stability and efficient nitrogen removal for digester supernatant.